Optical recording medium

Abstract

Optical recording media include substrates of a larger diameter formed by injection molding a copolymer of ethylene with a cyclic olefin. The media are adapted for high speed rotation with the benefits of a high output, high C/N, and low noise level. When a protective substrate of glass is attached to the polyolefin substrate such that the recording layer is inside, there is obtained a light-weight rigid disk which experiences minimal axial runouts and hence, minimal focusing errors during high rotational speed operation.

We claim: 
     
       1. An optical recording medium comprising a recording layer on a substrate having a diameter of at least 200 mm, wherein recording/reproducing operation is performed while rotating the medium at 1,800 rpm or higher, said substrate including a skin layer having a thermal softening point of 100 to 140 degrees C under the surface thereof bearing the recording layer, said substrate having the thermal softening point of the skin layer and a secondary thermal softening point higher by at least 10 degree C than the skin layer thermal softening point, said substrate being formed of a resin composition comprising at least one cyclic polyolefin obtained by copolymerizing ethylene with a cyclic olefin of the general formula: ##STR3##  wherein n is 0 or a positive integer, R 1  through R 12  are independently selected from the group consisting of a hydrogen atom, halogen atom, and hydrocarbon group, and R 9  through R 12 , taken together, may form a mono- or polycyclic group which may have a double bond, or R 9  and R 10  or R 11  and R 12  may form an alkylidene group.   
     
     
       2. The optical recording medium of claim 1 wherein said recording layer contains a dye, and said medium further includes a reflective layer on said recording layer. 
     
     
       3. The optical recording medium of claim 1 wherein said recording layer is formed directly on said substrate by a vapor phase deposition method. 
     
     
       4. The optical recording medium of claim 1 which further includes an undercoat layer between said substrate and said recording layer, wherein said recording and undercoat layers each are formed by a vapor phase deposition method. 
     
     
       5. An optical recording disk comprising a pair of resin and glass substrates, the resin substrate having a recording layer thereon and the glass substrate serving as a protective substrate, wherein said pair of substrates are joined into an integral disk such that the recording layer is inside, said resin substrate includes a skin layer having a thermal softening point of 100 to 140 degrees C under the surface thereof bearing the recording layer and wherein said resin substrate has the thermal softening point of the skin layer and a secondary thermal softening point higher by at least 10 degrees C than the skin layer thermal softening point, said resin substrate being formed of a resin composition comprising at least one cyclic polyolefin obtained by copolymerizing ethylene with a cyclic olefin of the general formula: ##STR4##  wherein n is 0 or a positive integer, R 1  through R 12  are independently selected from the group consisting of a hydrogen atom, halogen atom, and hydrocarbon group, and R 9  through R 12 , taken together, may form a mono- or polycyclic group which may have a double bond, or R 9  and R 10  or R 11  and R 12  may form an alkylidene group.   
     
     
       6. The optical recording disk of claim 5 wherein recording/reproducing operation is performed while rotating the disk at 1,800 rpm or higher. 
     
     
       7. The optical recording disk of claim 5 wherein said recording layer contains a dye, and said disk further includes a reflective layer on said recording layer. 
     
     
       8. The optical recording disk of claim 5 wherein said recording layer is formed directly on said resin substrate by a vapor phase deposition method. 
     
     
       9. The optical recording disk of claim 5 wherein said resin substrate is formed by injectionmolding the resin composition. 
     
     
       10. The optical recording disk of claim 5, further comprising an undecoat layer between said resin substrate and said recording layer, wherein said recording and undercoat layers are formed by a vapor phase deposition method.